An Assessment of the Contribution of Vehicular Traffic to Ambient Air Quality - A Case Study of Nairobi Expressway Corridor

In this study, the vehicular air pollution from the Nairobi Expressway corridor was estimated by simulation using AERMOD dispersion model. The Vehicle Kilometer Travelled (VKT), emission factors, and traffic data were used to estimate the pollutants from vehicular traffic.. The highest modelled 24-hour and annual concentrations of PM2.5 were 0.274 mu g/m3 and 0.152 mu g/m3, whereas the highest 24-hour and annual concentrations of PM10 were 0.405 mu g/m3 and 0.225 mu g/m3, respectively. The maximum 24-hour and annual concentrations of Total Volatile Organic Compounds (TVOCs) were 20.8 mu g/m3 and 11.5 mu g/m3, respectively, whereas the maximum 8-hour and annual concentrations of carbon monoxide (CO) were 319 mu g/m3 and 177 mu g/m3, respectively. The highest modeled 24-hour and annual concentrations of NO2 were 28.2 mu g/m3 and 15.7 mu g/m3, respectively. The 24-hour average measured TVOCs values showed that Nairobi expressway traffic contributed 3.5 percent to the measured TVOCs concentration value, but CO accounted for 55 percent of the measured value. According to the simulated PM2.5 and PM10 concentration values, Nairobi expressway traffic contributed 1.1 and 1.6 percent, respectively, to the 24-hour average measured concentration levels.